Chromatographic separation systems for separating valuable components, such as sugars and betaine, from plant-based extracts and hydrolysates and derivatives thereof, for example sulfite spent liquors, molasses, vinasse and starch hydrolysates, have been developed in recent years to improve the separation capacity and the separation efficiency of the systems. However, chromatographic separation systems, especially batch and also SMB systems, have the drawback that the ratio of eluent to feed has conventionally been rather high owing to the very complex nature of the systems. Various arrangements for circulating fractions of the eluate back to the separation system are already in use in chromatographic batch and SMB systems.
U.S. Pat. No. 4,109,075 (CPC International Inc.) discloses a process for separating saccharides for example from a starch conversion product by a batch chromatography method, wherein at least three different saccharide fractions with differing molecular weight are collected. The first saccharide fraction (the highest molecular weight fraction) is then used for elution of the next feed, followed by elution with water. It is recited that this mode of operation minimizes the amount of eluent water and produces fractions rich in any one of lower saccharides DP1 through DP4.
U.S. Pat. No. 4,267,054 (Sanmatsu Kogyo Co.) discloses a batch chromatographic separation process for separating two components (such as glucose and fructose) from a multicomponent mixture, where the eluate coming from the separation column is collected in four fractions (a), b), (c) and (d). Fractions (a) and (c) are product fractions, fraction (b) is a mixed fraction containing relatively large amounts of the target products, and fraction (d) comprises a dilute fraction of the tail of fraction (c) and the head of fraction (a) used in the next cycle of operation. Fractions (b) and (d) are returned to the separation system by introducing them to the top of the separation column.
U.S. Pat. No. 4,402,832 (UOP Inc.) discloses a process for separating an extract component (such as fructose) from a raffinate component (such as glucose) in an SMB chromatographic system, where a dilute extract fraction and an impure raffinate fraction are returned to the same column from which they are collected. It is recited that the process provides considerable savings in the energy required to recover the eluent from the product streams as compared to prior art processes. Furthermore, it is recited that a reduced rate of fluid circulation through the separating units is achieved, which enables denser packing of the columns. This, in turn, is recited to minimize channelling through the adsorbent bed and to minimize void volume.
U.S. Pat. No. 4,487,198 (Hayashibara) disloses a dual stage chromatographic batch process for separating maltose from sugar starch solutions, where the eluate coming from the separation column in the first stage is collected in five fractions A, B, C, D and E. Fraction A is a dextrin fraction, fraction C is a maltose fraction and fraction E is a glucose fraction. Fraction B is a rear slope fraction containing dextrin with maltose impurities, and fraction D is a front slope fraction containing maltose with glucose impurities. In the next stage, fractions B and D are sequentially in this order applied to the separation column together with a fresh feed so that fraction B is introduced before the feed and fraction D after the feed.
U.S. Pat. No. 6,200,390 (Amalgamated Research Inc.) discloses a chromatographic continuous SMB process for recovering betaine and sugars from molasses, for example. In this process, a “block” of betaine is displaced from the circulation loop of the SMB system without disturbing the normal operation of the system. In practice, a betaine-concentrated fraction is withdrawn from the circulation loop of the continuous SMB system while an equal volume of water is introduced into the circulation loop. The circulation loop then continues without disruption.
U.S. Pat. No. 6,602,420 (Amalgamated Research Inc.) discloses a twostep chromatographic separation process with coupled looping; including a simulated moving bed operation coupled with continuous displacement chromatography (continuous SMB). The process may be applied to the recovery of betaine and/or invert sugar from sucrose solutions, such as molasses, to enable the subsequent production of a high purity sucrose product. It is recited that the use of displacement rather than elution provides reduction in the quantity of the eluent. It is stated that typical molasses chromatographic separation systems use ratios of about 6.0 to 8.0 water volume for each volume of feed molasses (60% dissolved solids in the feed), whereas the application of displacement chromatography permits organic compounds (such as betaine) to be separated with water-to-feed ratios of 2.0 or less. Furthermore, the concentration of the betaine fraction is recited to rise from a typical range of 1 to 5% dissolved solids to a range of 8 to 15% dissolved solids.
U.S. Pat. No. 5,127,957 (Danisco) discloses a chromatographic sequential SMB method having at least three columns for separating betaine, sucrose and rest molasses from molasses during the same cycle (one loop). In one embodiment of the process, a new portion of feed solution is added to the column series between partly separated rest molasses and sucrose fractions to the top of a preselected column.
U.S. Pat. No. 6,093,326 (Danisco) discloses a chromatographic two-loop SMB method comprising at least two packing material beds for processing a beet molasses based solution to recover a betaine fraction and a sucrose fraction.
In addition to beet molasses, the molasses solution may be for example cane molasses, stillage, vinasse wood molasses, wheat molasses, barley molasses or corn molasses.
U.S. Pat. No. 6,896,811 B2 (Danisco) discloses a chromatographic SMB method for fractionating a solution into at least two fractions by circulating the formed separation profile more than once or less than once through the chromatographic separation loop during one cycle (before the next feed is supplied to the separation system). The method may be applied for example to the separation of xylose from sulfite cooking liquor, sucrose and betaine from beet molasses, fructose from a fructose-containing syrup and maltose from a maltose-containing syrup.
U.S. Pat. No. 5,637,225 discloses a method of separating xylose from a sulfite cooking liquor by a chromatographic sequential SMB system comprising at least two chromatographic sectional packing material beds. The liquor to be separated is recycled in a recycling phase in one or more loops comprising one or more sectional packing material beds.
U.S. Pat. No. 6,572,775 discloses a method of fractionating a solution into two or more fractions by a chromatographic simulated moving bed process, wherein the separation comprises at least two separation profiles in the same loop. The method may be applied to the separation of betaine and sucrose from molasses, betaine from vinasse, glucose and fructose from a glucose/fructose mixture, and xylitol from a xylitol run-off, for example.
It appears from the above-described prior art that it is known to return fractions comprising different parts of the separation profile back to the separation columns. It also appears that the known arrangements provide reduced amounts of the eluent, savings in the energy required to recover the eluent from the product streams as well as higher purities of target component fractions. However, a need still exists for a more versatile separation process, where parts of the separation profile containing different fast moving and slow moving components are introduced back into different positions of the separation system as an eluent substitute to reduce further concentration costs and to enable the recovery of the components in desired target fractions while essentially maintaining or even improving the yield and purity of the product components.